In this work oxidized and non-oxidized amorphous boron (a-B) powder was mixed with the elemental Mg in the atomic ratio 2:1 with the intent to mechanically synthesize the Mg(BH₄)₂ complex hydride. The blends were subjected to the controlled reactive mechanical alloying (CRMA) under hydrogen in a magneto-mill up to 200h. In effect, the particle size was refined to the 100-200nm range. Nanocrystalline MgH₂ (~6nm crystallite size) has been formed within the particles when an oxidized a-B is used. In contrast, a mixture of MgB₂ and an amorphous hydride MgH_x (a-MgH_x) has been formed when a non-oxidized a-B is used. The XRD pattern for the nearly-nanopowders containing non-oxidized a-B demonstrates the complete disappearance of the MgH₂ phase. Instead, the peaks rising above the background can be attributed to MgB₂. We are inclined to attribute it to the hydrogen evolution since desorption conducted in a Sieverts-type apparatus revealed ~1.4wt.% of hydrogen release. The XRD pattern for the powder after DSC test exhibited strong peaks from the MgB₂ phase. Oxide doping effect on the observed phase transformations is discussed.

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1. Synthesis of nanoparticles using electrical discharges.
2. "Synthesis of nanopowders by electric discharge assisted mechanical milling".
3. Formation and Processing of Nanocrystalline Materials by Electrical Discharge Mechanical Milling